The present invention relates to shaped organopolysiloxanes containing sulfonate groups which, in terms of process technology and performance, have the advantage of a macroscopic spherical shape in comparison to previously developed organopolysiloxanes containing sulfonate groups (DE 32 26 093 corresponding to U.S. Pat. No. 4,552,700 which is incorporated by reference). The present invention also relates to processes by which these new products can be produced, not only in the ideal particle size for the particular application described below but also with suitable physical properties. The present invention also relates to processes for using these shaped organopolysiloxanes.
Strongly acidic cation exchangers, of which the functional groups consist of sulfonic acid units, are used not only in the desalination, purification and softening of water and aqueous solutions and in the production of drinking water, but also and above all as a solid acid catalyst in chemical syntheses or as a support for metal catalysts (see Haag et al., DE-OS 18 00 371; W. Neier, Chem. Ind. 33, (1981), page 632). The types used almost exclusively in the catalytic field always consist in principle of an organic, partly crosslinked polystyrene skeleton to which the sulfonate groups are attached by the phenyl rings.
Commensurate with this structure, the physical and chemical properties of these cation exchangers are forged by the organic character of the polymer backbone which gives rise to a number of performance-related disadvantages, such as a relatively low heat resistance of 100.degree. to 130.degree. C., an occasionally high sensitivity to chemical attack and bacterial contamination which can culminate in complete degradation of the matrix, solubility in certain solvents under drastic conditions, strong swellability and dependence of the exchanger volume upon the ambient medium, the need for swelling to make the functional groups accessible and, hence, non-useability in certain organic solvents.
Although inorganic polymer systems (e.g., silica gel) have the advantages of a fixed and rigid structure, non-swellability, high heat and ageing resistance, insolubility in organic media and water (see EP 0 008 902; GB 1,506,226), cation exchangers in the H.sup.+ form produced on this basis only have a maximum capacity of 0.5 to 0.6 meq/g on account of the relatively small number of functional groups. In addition, since--for steric reasons--the SO.sub.3 H--bearing groups are only anchored to the support surface by a maximum of 1 to 1.5 siloxane bonds, they are always in danger of breaking free. The prior art on ion exchangers in general is described in synoptic form, for example, in Ullmanns Enzyklopadie der techn. Chemie, 4th Edition, Vol. 13, page 29. Information on acid catalysis using acidic ion exchangers is provided by H. Widdecke in British Polymer Journal (1984), Vol. 16, pages 188 to 192.
DE-PS 32 26 093 (U.S. Pat. No. 4,552,700) describes organopolysiloxanes containing sulfonate groups which may also be used as solid acid catalysts, which have an organopolysiloxane backbone resistant to partial or complete dissolution in aqueous media, and in which the sulfonate groups are anchored to the matrix by organic spacer groups. These systems enjoy the advantages of an inorganic polymer backbone and have a relatively high capacity for sulfonate groups of which the anchorage is guaranteed by an Si atom incorporated in the matrix by a trivalent bond. In addition, the matrix of these polymers may be modified and adapted to meet requirements by the incorporation of non-functional silicon, titanium and aluminum units. However, the fact that the macroscopic appearance of these products is unsatisfactory has hitherto proved to be unfavorable because these polymers are present as asymmetrical coarse or fine particles and not in the applicationally favorable spherical form. In addition, their physical and morphological properties are not optimal.